Prometheus: Do not drop errors in streaming parser (grafana#57698)

- Fixes grafana#57692
- and also takes care of grafana#42776 when using the streaming parser, not an ideal fix for grafana#42776 but makes explore work better I think. grafana#57365 might be a better longer term solution

pkg/tsdb/prometheus/querydata/request.go

@@ -2,6 +2,7 @@ package querydata
 
 import (
 	"context"
+	"fmt"
 	"net/http"
 	"regexp"
 	"time"
@@ -112,19 +113,27 @@ func (s *QueryData) fetch(ctx context.Context, client *client.Client, q *models.
 		Error:  nil,
 	}
 
-	if q.RangeQuery {
-		res, err := s.rangeQuery(traceCtx, client, q, headers)
+	if q.InstantQuery {
+		res, err := s.instantQuery(traceCtx, client, q, headers)
 		if err != nil {
 			return nil, err
 		}
+		response.Error = res.Error
 		response.Frames = res.Frames
 	}
 
-	if q.InstantQuery {
-		res, err := s.instantQuery(traceCtx, client, q, headers)
+	if q.RangeQuery {
+		res, err := s.rangeQuery(traceCtx, client, q, headers)
 		if err != nil {
 			return nil, err
 		}
+		if res.Error != nil {
+			if response.Error == nil {
+				response.Error = res.Error
+			} else {
+				response.Error = fmt.Errorf("%v %w", response.Error, res.Error) // lovely
+			}
+		}
 		response.Frames = append(response.Frames, res.Frames...)
 	}